opencv画出轮廓外接矩形

     Mat cannyImage;
     /// Detect edges using canny
     Canny(src, cannyImage, , , );
     vector<vector<Point> > contours;
     vector<Vec4i> hierarchy;
     /// Find contours
     findContours(cannyImage, contours, hierarchy, CV_RETR_EXTERNAL /* CV_RETR_EXTERNAL CV_RETR_LIST CV_RETR_CCOMP RETR_TREE CV_RETR_FLOODFILL*/, CHAIN_APPROX_SIMPLE, Point(, ));

     /// Approximate contours to polygons + get bounding rects and circles
     vector<vector<Point> > contours_poly(contours.size());
     vector<Rect> boundRect(contours.size());

     for (size_t i = ; i < contours.size(); i++)
     {
         approxPolyDP(Mat(contours[i]), contours_poly[i], , true);
         boundRect[i] = boundingRect(Mat(contours_poly[i]));
     }